One method of packaging integrated circuit chips formed on semiconductor chips is through the use of a polyimide film similar to photographic film that is used as a base for the interconnect wires which are routed from other circuitry to the bond pads on the semiconductor chip. The polyimide films may comprise, for example, Upilex or Kapton. A chip is initially placed in an inner opening in the film and interconnects are routed from the bond pads on the chip to test pads on the periphery of the film. The inner opening is surrounded by an inner polyimide ring. Four outer openings surround the inner polyimide ring. The interconnects are routed from the chip over the inner ring and then over the outer openings to the periphery of the film. The inner ring is coupled to the periphery of the film by four corner members of the polyimide film. After testing, the polyimide film and the interconnects are cut outside of the outer openings and the combination of the film, the interconnects and the chip is mounted to a circuit board so that the chip may be used for its intended purpose.
The leads that are routed from the chip over the film are extremely thin and fragile. The chips are required to operate in environments with dramatically changing temperature. For example, some chips are tested in the temperature range on the order of -65.degree. C. to 150.degree. C. The difference in thermal coefficient of expansion between the film and the semiconductor material such as silicon which is used to form the integrated circuit chip creates stresses on the leads passing from the chip over the film. This stress can be great enough to cause delamination between the leads and the film and in catastrophic cases, breaking of the leads.
For smaller die sizes, the spacing between the integrated circuit chip and the inner ring of polyimide film can be increased to reduce the stress on the leads. However, as die sizes increase, this approach becomes impractical. Accordingly, a need has arisen for a new form of tape automated bonding packaging which eliminates the problems with lead breakage and delamination caused by differences in the thermal coefficient of expansion between the semiconductor material and the film material.